Hygrometric device



April 5, 1949. P. A. HILTZ 2,466,658

HYGROMETRIC DEVICE Filed Jan. 25, 1946 2 Sheets-Sheet l I "ill/I111] 2 4 a I N V EN TOR.

A r l 5, 1949. P. A. HILTZ 2,4 6,656

HYGROMETRIC DEVICE Filed Jan. 25, 1946 2 Sheets-Sheet 2 1 H-HH- #6....

Patented Apr. 5, 1949 HYGROMETRIC DEVICE Paul A. Hiltz, Somerville, Mass., assignor to Serdex, Inc., Boston, Mass,

Massachusetts a corporation of Application January 25, 1946, Serial No. 643,430

4 Claims. 1

My invention relates to hygrometry and consists in a hygroscopic unit of improved sensitivity, power, and repeatability.

Hitherto it has been customary to employ a bundle of hairs or an elongated strip of animal tissue for the hygroscopic element in a hygrometric instrument. However, instruments heretofore available have been notoriously inaccurate and unsatisfactory. The principal diiliculty encountered has been the lag, or hysteresis, which introduces an error of about That is to say,whenthehumidity increases or decreases substantially and then returns to its original value, the reading will be found erroneous by that amount. Furthermore in order to gain power sufficient to actuate recording apparatus the bundle of hairs or strip of tissue has had to be widened with considerable sacrifice in sensitivity.

The primary object of my invention is to improve the accuracy and power of hygrometric instruments and particularly to eliminate erroneous reading due to the effect of hysteresis.

Another object of my invention is to provide improved hygrometric apparatus for radiosonde recorders, recording hygrographs, hygroscopes,

hygrometers, and various types of telemetering instruments requiring the use of humidity data.

The most important feature of my invention resides in a diaphragm of goldbeaters skin tightly stretched over a ring in combination with an indicator bearing on the diaphragm and movable in response to changes in the tautness of the diaphragm caused by variations in the atmospheric humidity to which it is exposed.

These and other objects and features of my invention will be more readily understood and appreciated from the following detailed description of a preferred embodiment thereof selected for purposes of illustration and shown in the accompanying drawings, in which I Fig. l is a view partly in perspective and partly in cross-section of a diaphragm constructed in accordance with the invention,

Fig. 2 is a view in vertical cross-section through an instrument embodying the invention,

Fig. 3 is a view in cross-section through a sec-- ond embodiment of the invention, and

Fig. 4 is a view in cross-section through a portion of a third embodiment of the invention.

For the hygroscopic material I use goldbeaters skin, i. e. the membrane of the large intestine of the ox. To support the membrane I provide an outer ring ill of brass or other metal having a pcripheral flange [2 of reduced thickness provided with a series of screw holes l4, and an inner peripheral flange [B of reduced thickness provided with a series of threaded holes l8. An inner metal ring 20 fits snugly on the flange 16. I stretch over the outer ring ID a sheet 22 of gold beaters skin and press the inner ring 20 into position on the fiangelfi. Subsequently I screw the rings together with a series of screw 24 which are received in the threaded holes 18. Thus, there is formed a circular diaphragm 22 of goldbeaters skin maintained under radial tension and confined throughout its margin. The excess protruding between the rings is trimmed ofi flush with the tops of the rings l0 and 20. The degree of radial tension imposed on the diaphragm is determined in advance by the amount of tension exerted on the goldbeaters skin before the rings are pressed together. It is important to note that the edge of the diaphragm is confined throughout and that there is no portion thereof which is free to move.

There is an infinite variety of ways in which the hygroscopic element thus produced may be employed in practice. I have suggested three possible instruments in Figs. 2-4.

In Fig. 2 there is provided a cylindrical metal case 30 having one open end to which the hygroscopic unit is secured by means of a series of screws 26 which pass through the holes M in the outer flange of the ring l0. Disposed in the center of a closed end of the case 30 is a boss 32 containing a large axial socket 34 and a smaller coaxial socket 36. A rod or finger 38 extends into both sockets and has on its outer end a rounded button 39 hearing against the center of the diaphragm 22. Within the socket 34 and surrounding a portion of the finger 38 is a compression spring 4!] which bears against the bottom of the socket 34 and a stop 42 formed on the rod 38.

At an intermediate point the rod 38 is provided with a transverse pin 44 received on either side in a slot formed in the forks of a clevis at one end of an arm 45. The upper end of the arm 45 is mounted on a pivot pin 46 secured in a hollow boss 48 extending into the case 30 and contain- 3 ing an arm or pointer 50 with the arm 45.

In operation the pointer 50 swings in accord-' ance with changes in the tension or tautness of the diaphragm 22. That is to say, if the hu- 5 midity decreases the tension of the diaphragm increases, since the goldbeaters skin shrinks as it dries.

In Fig. 3 I have shown another embodiment of the invention. Here again a diaphragm 22 is confined by a pair of rings I0 anda and secured to a cylindrical case-60=- A bracket I52 secured to the Wall of the case60 provides a'pair of bearings 64 in which slides a rod 68 secured at one end to a grommet I0 set in the center of the dia-" phragm 22. The other end of the rod 68 is pierced to receive one end of a tension spring'-"l2; The" outer end of the spring I2 is hooked into the end; of a plunger I4 received in a'socketin the-case I50 and slotted to fit a key I6 which prevents rotation of the plunger. A set screw I8 is threaded into the end of the plunger wand bearsagamst the case 60 to provide mean-s for adjusting .the tension of the spring 12.

A pin 82 is set into the rod 68 at an intermedi'ate point and works in slots romeo in a clev'is 80"on the end of an armaa. A bracket'B I is mounted in the case 60'andcarri'es' at its inner 'end' ai'pivot pin 86 on which the arm 83 is mounted." The'upper endof the arm-'83 terminates in a gear segment 88 meshing witha pinion 90' keyed to "a pointer 92 pivotally mounted on a 1ug'94 and extending from the case fiflthrough a slot 96 which incidentally equalizes atmospheric pressure at all" times within and without the case 60.

The operation of the device shown in Fig. 3 is analogous to that shown in Fig. 2.- However the grommet I0 provides a more p'ositiveco'nnection" between the diaphragm 22""andthemechanicallinkage. in response to changes in humidity the'rod 68 is moved axially against the spring I2; The movement of the rod 68" is transmitted"- through the arm- 83 and the gearing to'the pointer92. It is to be'understood that the I well as the pointer'50 in Fig. 2 maybe connected to anysuitable recordingapparatus or be arranged to playacross the face of a suitably calibrated dial.

In Fig. 4 I have suggested a construction-in which the diaphragm is coupled with an electric recording 'orindicating circuit. In'this'case the diaphragm 22 of goldbeaters skin isagain confined between a pair of rings I0 and 20. A'case I00 is provided with an integral socket receiving aspring I0I which surrounds'a portionof a rod or finger I02 provided at its inner end with a rounded button I04 bearing against the diaphragm 22. The rod extends through the wall of the 'case I00 and terminates in a reduced portion carrying an iron cylinder I06 received in an axial bore formed in a coil support I08 of dielectric material- A coil IIO of insulated wire is wrapped abouttheexterior of-the support I 00 and forms part of an electrical indicatingor recording: circuit of conventional'design. A gasket H2 of: insulating material is interposed between the coil support I 08 and the case I00, andthesupportis secured to thecase by means of a series of screws I IB' received in insulating bushings II4.-= The bushings H4 and the gasket H2 effectively insula't'the support I08 from the case I00. I The cylinder I06 thus forms themovable core for the-coil- IIO, and the axial movement of the core I0 0 inrespon'se'to the'ch'ange in tension on the diasecured to or integral As the "diaphragm contracts or extends" pointer 92 inFig. 3 as 1;,

phragm 22 varies the inductance of the coil H0. The variations in inductance of the coil '0 are used to actuate recording or indicating instrumentalities coupled to the circuit. While I have shown structure for varying inductance of a coil included in the circuit, it will be understood that the rod I02 may also be connected to means for varying capacitance, resistance, or other impedance in any number of suitable circuits. Inasmuch as the type of circuit used depends upon the location of the apparatus, the type of power available, and the use to which the apparatus is to be put, I have'not shown thedetails of any one circuit.

Apparatus of the type herein illustrated and described oifers several advantages over hygroscopic elements heretofore in use. In the first place the fact that the entire periphery of the diaphragm is confined and the entire diaphragm subjected-to equal tension, results in greatly increased sensitivity as well as greater extension. Furthermore the construction herein shown prevents errors due to hysteresis, particularly by eliminating the undesirable effects which occur when shrinkage takesplace and portions of the edge are free to move. A strip of goldbeaters skin of of an'inch Wide and confin'ed'only" atits' ends will exhibit an error of at least 5% plus" or minus. By using'a 2% or 1 /2 diameter diaphr'agm of the type herein shown, the error in"- calibration is reduced to less than plu's'or" minus. As regards the pow'er'available, I'h'ave? found that a 2 diameter diaphragm expands of an inch and a 1 diaphragm expands" m'ore than of an inch for a given degree'ofj change in humidity. This with the extension obtained from' a'strip of goldbeaters skin of an inch wide and3" long. Im the latter case the maximum extension is only 2;; of an inch. Thus it will be seen that the dia phragm of my invention not only increases the accuracy and sensitivity of hygrometric devices but materially increases the mechanical power available for the actuation of measuring or indicating devices.

Having now described and illustrated several]. preferred embodiments of my invention what' I claim-as new and desire to secure by Letters Patent of the United States is:

1. A hygrometric instrument which comprises acircular diaphragm of hygroscopicgoldbeater s skin, means including a casing for holdingtheentire diaphragm under radial tension While exposed on both faces to atmospheric conditions;--. and means acting on the diaphragm within the; casing for indicating changes of tension thereincaused by variations in atmospheric humidity.-

2. A hygrometer comprising a pair of fiat rig-id annuli, a diaphragm of goldbeaters skin clamped marginally between said annuli, a spring loaded. mechanism coupled to the center of the-die phragm and subjecting the diaphragm to prede'w :termined radial tension and'indicating means: connected to and actuated by said-diaphragm.

3. In a hygrometer including an indicator and mechanism for moving the indicator, a hygrometric element comprising a diaphragm of goldbeaters skin, an open frame confining the-.entire periphery of said diaphragm and exposing; bothfacesthereof to theatmosphere, and means mechanically coupling said diaphragm. to the-- mechanism and for tensioning said diaphragm:

4. In a hygrometer including a movable memw her, a hygrometric element comprising a diaphragm of goldbeaters skin, a frame confining may be contrasted" REFERENCES CITED The following references are of recerd in the file of this patent:

UNITED STATES PATENTS Number Name Date 127,752 Emery June 11, 1872 248,183 Klinkerfues Oct. 11, 1881 Number Number Name Date Duwelius May 21, 1901 Hemberger Sept. 22, 1908 Ballard Feb. 28, 1911 Elfering May 9, 1916 Miller Sept. 12, 1933 Bristol May 15, 1934 McDonnell Feb. 16, 1937 Shurtleff Feb. 23, 1937 FOREIGN PATENTS Country Date Great Britain Nov. 24, 1927 Great Britain Feb. 7, 1944 

